The screen blanking with M1 was driving me crazy. I went through untold amount of cables, and ended up with miniDP (on the dock) to DP (on the monitor) that doesn't blank, but only flickers occasionally.

The funny thing is that 2015 Intel MBP (with Apple TB2->TB3 adapter) with the same dock and same monitor didn't blank or flicker. I guess it is something about the new Apple TB implementation in M1.